There has heretofore been known a drive apparatus of a vehicle including a differential mechanism through which an output of a drive power source, such as an engine or the like, is distributed to a first electric motor and an output member, and a second electric motor disposed between the output member and drive wheels. Such drive apparatus for a hybrid vehicle is disclosed for example in Patent Publication 1. The drive apparatus includes a differential mechanism being comprised of a planetary gear unit i.e., gear set and performing as the differential action for mechanically transmitting a major part of power outputted from the engine to drive wheels. A remaining part of power from the engine is electrically transmitted from the first electric motor to the second electric motor using an electrical path.
Thus, the drive apparatus operates as a transmission of which shifting ratio i.e., gear ratio is electrically changed, for example as an electrically controlled continuously variable transmission. The drive apparatus is controlled by the control device so that the vehicle runs i.e., is driven with the optimum operation state of the engine, thus improving fuel consumption, i.e., mileage.
Patent Publication 1: JP 2003-301731
In general, the continuously variable transmission has heretofore been known as a device for improving fuel consumption of a vehicle. A gear type power transmitting device such as a step variable automatic transmission has heretofore been known as a device having high transmitting efficiency. However, no power transmitting mechanism having such combined advantages has been put into practical use yet. For instance, the hybrid vehicle drive apparatus, disclosed in the above Patent Publication 1, includes the electrical path through which electric energy is transmitted from the first electric motor to the second electric motor, that is, a transmitting path through which a part of the vehicle drive force is transmitted in the form of electric energy. This inevitably causes the first electric motor to be made large-size with an increase in an output of the engine. Also, the second electric motor, driven with electric energy output from the first electric motor, is caused to increase in size. Thus, an issue arises with the occurrence of an increase in size of the drive apparatus.
Alternately, the part of the engine output is transmitted to the driving wheel after converted to the electric energy once, which may worsen the mileage depending on the vehicle running condition such as the high speed running i.e., driving. Similar problem may occur when the above power distributing mechanism is used as the continuously variable machine called the electrically controlled CVT in which the shifting ratio is electrically changed.
With the drive apparatus for hybrid vehicle disclosed in Patent Publication 1, further, there has heretofore been known a transmission incorporated in a power transmitting path between an output member of a differential mechanism (electrically controlled continuously variable shifting transmission) and drive wheels with a view to minimizing a required capacity of the second electric motor to meet a need for increasing drive torque. With such a drive apparatus for vehicle, an output of a drive power source is transferred to the drive wheels via two shifting mechanisms including the electrically controlled continuously variable shifting transmission and the transmission, while permitting the drive apparatus to establish a total gear ratio based on respective gear ratios of the shifting mechanisms.
When this takes place, if the transmission executes the shifting, then, a need arises to execute the control of the continuously variable transmission with such a shifting. This causes likelihood of the transmission and the continuously variable transmission complicated in control, unlike the transmission and the continuously variable transmission are provided independently for respective controls, resulting in the occurrence of shifting shocks.
As one example of the transmission, a step variable automatic transmission (hereinafter referred to as “step variable transmission”) has been known including a engaging device for selectively engaging plural sets of rotary elements of a planetary gear set to be alternatively switched to plural gear positions such as a forward 4th-gear, a forward 5th-gear and a forward 6th-gear, etc. With such a step variable transmission, an engaging pressure of the engaging device is controlled during a shifting so as to suppress the shifting shocks. However, the engaging pressure of the engaging device needs to be controlled in conjunction with a control of the continuously variable transmission during the shifting of the step variable transmission. Accordingly, there has been likelihood of the transmission and the continuously variable transmission more complicated in control than that independently executed by the step variable transmission, resulting in the occurrence of shifting shocks.
Further, with a vehicle drive apparatus having a transmission provided in a power transmitting path between an output member of a differential mechanism and drive wheels with a view to addressing the issues of the drive apparatus for hybrid vehicle described above, likewise, there has been a probability of shifting shocks being caused to occur.
With the drive apparatus for hybrid vehicle described above, further, there has been well known a type in which the transmission is provided in the power transmitting path between the output member of the differential mechanism (electrically controlled continuously variable shifting transmission) and the drive wheels. With the drive apparatus for hybrid vehicle of such a type, for instance, a step variable transmission is disposed in the power transmitting path between the output member of the differential mechanism and the drive wheels with a view to decreasing a required capacity of a second electric motor when increasing drive torque is demanded for thereby miniaturizing the second electric motor.
With the step variable transmission structured to switch the gear positions i.e., shift position upon engaging and disengaging the engaging device, in general, respective engaging pressures of an on-disengaging side engaging device and an on-engaging side engaging device are uniformly set depending on engine torque. This is because a balance is provided between the suppression of the shifting shocks and the shortening of the shifting time in consideration of durability or the like of the engaging devices. Alternately, the engaging pressures are learned based on an input rotation speed applied to the step variable transmission during the shifting thereof. The input rotation speed varies at a predetermined rate so as to provide the balance between the suppression of the shifting shocks and the shortening of the shifting time, in consideration of durability or the like of the engaging devices.
Further, the differential mechanism performs a differential action enabling a first electric motor and/or a second electric motor to be used for controlling the engine rotation speed at an arbitrary rotation speed regardless of, for instance, a rotation speed of an output shaft, and controlling the rotation speed of the output shaft at an arbitrary rotation speed regardless of the engine rotation speed.
With the drive apparatus having the two shifting mechanisms such as the differential mechanism and the step variable transmission, as the step variable transmission executes the shifting, the continuously variable transmission may be controlled in conjunction with such a shifting being executed. In this case, unlike a structure in which the transmission is independently provided with a learning control performed for learning the engaging pressure of the engaging device associated with the shifting, there has been likelihood of such a learning being complicated. In other words, like the structure in which the transmission is independently provided, if the engaging pressure of the engaging device, associated with the shifting, is uniformly learned and controlled, there has been a provability of a difficulty encountered in accurately obtaining a learning result.
The present invention has been completed with the above view in mind and has an object to provide a control device for use in a vehicle drive apparatus, having a differential mechanism operative to perform a differential action for distributing an output of an engine to a first electric motor and an output shaft and an electric motor disposed in a power transmitting path between the differential mechanism and drive wheels, which can miniaturize the drive apparatus or achieve improved fuel consumption while enabling the suppression of shifting shocks.
Further, it is another object of the present invention to provide a control device for a vehicle drive apparatus, having a differential mechanism operative to perform a differential action for distributing an output of an engine to a first electric motor and an output shaft, an electric motor disposed in a power transmitting path between the differential mechanism and drive wheels, and a transmission forming part of the power transmitting path, which enables an accurately learning of a engaging pressure of a engaging device associated with a shifting of the transmission.